45 Questions
What happens to the conduction velocity in certain cells?
It becomes progressively slower
What happens to the membrane potential in hyperkalemia?
It becomes less negative
What is the correct order of the conduction system in the heart?
SA node – AV node – Bundle of His – Purkinje fibers
What can cause fast responses of cardiac muscle to change to slow responses?
Hypoxia due to ischemia
What is the result of a lack of blood supply to a region of cardiac muscle?
Ischemia
What is the starting point of the conduction of the heart?
SA node
What can happen to the fast sodium channels in high potassium levels?
They are inactivated
What can be a consequence of hyperkalemia?
Arrhythmias and death
What can cause a region of cardiac muscle to become ischemic?
Coronary artery disease
What is the velocity of action potentials spreading throughout the atria?
0.5 m/s
What is the function of the AV node in the cardiac conduction system?
To slow down the impulse conduction
What is the region where the AV node is located?
Inferior-posterior region of interatrial septum
What is the characteristic of the AV node?
Highly specialized conducting tissue
What happens to the impulse conduction velocity in the AV node?
Decreases from 0.5 m/s to 0.05 m/s
What is the characteristic of the N region of the AV node?
Displays post repolarization refractoriness
What is the function of Bachmann's bundle?
Conducts impulses from the SA node directly to the left atrium
How do impulses from the SA node spread in the right atrium?
Radially throughout the right atrium along the ordinary myocardial fibers
What is the sequence of cardiac electrical activation?
SA node → Atria → AV node → Ventricles
What is the responsible ion for the start of rapid upstroke of the QRS depolarization in Phase 0?
Na
What type of cardiac fibers are responsible for producing fast-response action potentials?
Atrium, ventricles, and Purkinje fibers
What is the duration of the action potential in fast-response cardiac fibers?
Longer due to the plateau phase
What happens to the inside of the cell during Phase 0?
It becomes more positive
What is the role of the plateau phase in fast-response cardiac fibers?
Allows for ventricular filling
Which phase corresponds to the ST segment of the ECG?
Phase 2
What is responsible for the relatively prolonged duration of the cardiac myocyte electrical cycle?
Balance between Ca++ and K+
What is a characteristic of slow-response cardiac fibers?
The resting potential is less negative
Which phase is absent in slow-response cardiac fibers?
Phase 1
What happens to most fast Na+ channel gates during Phase 2?
They close
What is true about the ERP (Effective Refractory Rate)?
Fast sodium channels are inactivated
What is the result of the balance between the inward flow of Ca++ and outward flow of K+ in Phase 2?
No net current flow between cells
What happens to some K+ ions during Phase 2?
They exit the cell through slow K+ channels
What is the function of the ERP (Effective Refractory Rate)?
Prevents the heart from having compounded action potentials
What is the purpose of the plateau phase in fast-response cardiac fibers?
Allows for ventricular filling and prevents compounded action potentials
What happens to some Ca++ ions during Phase 2?
They enter the cell slowly through slow channel gates
What is the difference between fast-response and slow-response cardiac fibers?
Fast-response has a longer duration of action potential
What happens to repolarization by the end of Phase 2?
It continues
What is responsible for the plateau of the ventricular action potential?
A slow inward Ca2+ current
What is the result of an outward K+ current in cardiac tissues?
Repolarization of the cell membrane
What is responsible for the pacemaker property of sinoatrial (SA) nodal cells?
An increase in Na+ conductance
What is Phase 4 in cardiac tissues?
Electrical diastole
What is the function of gap junctions in cardiac tissues?
To provide low-resistance sites of current spread
What type of current is responsible for the upstroke of the action potential in the sinoatrial (SA) node?
A rapid inward Ca2+ current
What is the result of an increase in Na+ conductance in sinoatrial (SA) nodal cells?
Depolarization of the cell membrane
What type of current is responsible for the pacemaker property of sinoatrial (SA) nodal cells?
An inward Na+ current
What is the role of the sinoatrial (SA) node in the heart?
To generate the heartbeat
This quiz covers the physiology of cardiac fibers, including fast-response cardiac fibers, action potential, and phases of depolarization and repolarization.
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